1. Field of the Invention
The present invention relates generally communications, and more specifically to a wireless position location and tracking system.
2. Description of the Related Art
There is a well-established demand for the ability to track the location of various objects and/or persons within various environments. Owners of various assets may want to be able to locate those assets with precision at any time, in order to make efficient use of them (i.e. for deployment or re-deployment in response to varying demand). Security applications may include locating missing equipment, or preventing the loss of equipment.
Satellite tracking systems, such as the Global Positioning System (GPS), and others, may be used to provide location determination around the globe. Satellite tracking systems generally do not perform well inside buildings, or in other locations where the satellite signals are not readily receivable.
Radio Frequency Identification (RFID) systems are being developed to track and locate items within defined areas. Passive RFID systems are limited to detecting the presence of an item within range of a portal. Typically, a portal or interrogator sends out a query signal and any tag (i.e., a device included in or attached to an object to be tracked) within range responds. Passive RFID tags generally do not have a power source.
Active RFID systems function in a similar manner, but the active tags have a power source, typically a battery, for longer range operation. RFID systems (active and passive) require installing a dedicated infrastructure of portals or interrogators for tracking which may be difficult or expensive to deploy, and may lack flexibility.
Other systems employ RF fingerprinting, whereby mobile devices measure signal strength from one or more beacons and attempt to correlate those measurements with signature measurements taken throughout the defined area. One example is the RADAR system. (See P. Bahl and V. N. Padmanabhan, “Radar: An In-Building RF-based User Location and Tracking System”, in Proceedings of the IEEE Infocom 2000, Tel-Aviv, Israel, vol. 2, March 2000, pp. 775-784). One drawback of systems such as these is that the signature measurements are taken infrequently, and the measurement task may be cumbersome and expensive. The RF environment may change significantly throughout any given time period, and the accuracy of the location calculation will be degraded accordingly.
Other systems employ triangulation, whereby fixed devices measure the signal strength or propagation delay of a mobile device and use this information in conjunction with the known location of the fixed device to compute the location of the mobile device. These systems require installing a dedicated infrastructure of fixed devices for tracking, which may be difficult or expensive to deploy, and may lack flexibility.
There is therefore a need in the art for an accurate position location and tracking system suitable for a wide range of facilities in variable environments.